1. Field of the Invention
The present invention relates to a semiconductor light emitting diode, and more particularly, to a semiconductor light emitting diode having a textured structure to improve light extraction efficiency, and a method of manufacturing the same.
2. Description of the Related Art
A light emitting diode (LED) converts electrical energy into infrared rays or visible light using the characteristics of a compound semiconductor. The light emitting diode is a kind of electroluminescent (EL) device, and presently, the most widely used light emitting diodes employ an III-V group compound semiconductor.
The III-V group compound semiconductor is typically formed on a substrate formed of sapphire Al2O3. To improve light emission efficiency, or light extraction efficiency, various LED structures have been proposed. Current studies use a textured structure on a light extraction region of the LED to improve the light extraction efficiency.
Travel of light through an interface between material layers having different refractive indexes is limited by the refractive indices of the material layers. With a flat interface, when light passes from a semiconductor layer having a high refractive index into an air layer having a smaller refractive index (n=1) for instance, the light must enter the flat interface less than a predetermined angle with respect to the normal. If the light enters at an angle greater than the predetermined angle, the light is totally internally reflected at the flat interface, thereby greatly reducing the light extraction efficiency. To avoid the total internal reflection of light, a method of incorporating a textured structure at the interface has attempted.
FIGS. 1A and 1B are cross-sectional views illustrating a conventional light emitting diode having a textured structure. Referring to FIG. 1A, a p-GaN layer 102, an active layer 103, an n-GaN layer 104 are sequentially formed on a p-electrode 101, and an n-electrode 105 is formed on the n-GaN layer 104. When light generated by the active layer 103 is extracted upward through the n-GaN layer 104, a textured structure 106 is incorporated at an interface between the n-GaN layer 104 and the air layer to change the incidence angle of the light.
Referring to FIG. 1B, an n-GaN layer 112 is formed on a sapphire substrate 111, and an n-AlGaN layer 113, an active layer 114, a p-AlGaN layer 115, a p-GaN layer 116, and a p-electrode 117 are sequentially formed on a region of the n-GaN layer 112. An n-electrode 118 is formed on a region of the n-GaN layer 112 where the n-AlGaN layer 113 is not formed. This is a flip-chip structure, in which light generated by the active layer 114 is mainly extracted through the transparent sapphire substrate 111. Here, the light extraction efficiency is improved by forming a textured structure 120 on the surface of the sapphire substrate 111.
A conventional semiconductor light emitting diode incorporates the textured structure 120 to improve the light extraction efficiency. However, particularly as depicted in FIG. 1B, when a GaN group compound semiconductor layer is formed on the sapphire substrate 111, defects can be caused by the unmatched crystal lattice between the sapphire substrate 111 and the GaN group compound semiconductor layer, and can spread to the active layer. The internal crystal defects in the GaN group compound semiconductor layer can reduce the light extraction efficiency. Accordingly, a new type of semiconductor light emitting diode is needed, that can reduce crystal defects and increase the light extraction efficiency.